1. Field of the Invention
The present invention relates in general to the field of cable connection error detection. More particularly, the present invention relates to an improved electrical means for detecting the misconnection of cables.
2. Background Discussion
The great number of circuit boards used in today's electronic digital computers require many cables, usually of the multi-line ribbon type, for interconnection between the boards and from boards to the computer mainframe itself. When a computer is installed, or after it has had its boards removed for servicing, scores of these cables must be connected. Due to the great number of these cables, as well as the symmetrical shape of a typical ribbon cable and connector, it is quite easy for an installer to wrongly connect one or more cables.
There are many types of cabling errors which may be committed when installing cables. For example, an installer may connect one end of a cable properly to a socket on one board, then unintentionally twist the cable before connecting the other end to the other socket on another board. This results in improper connection between the two sockets, and hence may be called a "twisted cable" error. Another common error results when an installer connects a cable between the wrong two sockets. This is referred to as a "misplugging error." Yet another type of error occurs when the installer connects the cable to two sockets on the same board, rather than from a socket on one board to its corresponding socket on another. This is referred to as a "reversed plugging" error.
It is easily seen that any of the above errors, which can occur separately or in combination, will result in a faulty correspondence between the subsockets of each interconnected socket. This will usually result in faulty operation of the computer. To prevent this faulty operation, a number of schemes have been devised to detect proper connection of cables.
One scheme for detecting the proper connection of cables is a mechanical technique. This involves the use of "keying". In essence this involves providing special markings for each cable connector pair. This mechanical technique may assist in preventing the improper connection of cables. However, the mechanical technique does not detect these errors should they occur.
Another scheme involves inputting data at the pins of a cable at the driving end, transmitting this data through the cable into the board into the receiving end of the cable, and reading this data out of the board at the receiving end. One technique employs scan registers at both ends of the cable. With this technique, a pattern is scanned into one end of the cable, clocking occurs and the results are scanned out at the other end of the cable and essentially compared with expected results. However, one of the problems with this scan technique is that it can only be used in systems which have scan functionality incorporated therein. It is typical for only more complicated computer systems to use such scan hardware. Moreover, the scan technique does require substantial extra hardware. Furthermore, this technique requires using the valuable processing time of the computer for the performance of a rather mundane task.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for cable connection errors which requires the use of little additional hardware and processing time and which can be relatively inexpensively implemented.
Another object of the present invention is to provide an improved method and apparatus for detecting proper and improper connection of cables and in which this is carried out essentially automatically so that whenever a cable is plugged in improperly there is an immediate automatic detection thereof.